To date, the only extant detailed abundance analyses of
elements for Galactic
bulge stars are by
McWilliam & Rich
(1994)
and A McWilliam, A Tomaney & RM Rich in preparation).
McWilliam & Rich
(1994)
found that Mg and Ti are enhanced by ~ +0.4
dex in almost all bulge stars, even at solar [Fe/H]; however, the abundances
of Ca and Si appear to follow the normal trend of
/ Fe ratio with [Fe/H]
(see Figure 5).

Figure 5. Trends of
-element abundances in
the Galactic bulge, from
McWilliam & Rich
(1994).
Filled triangles indicate the average [(Mg+Ti)/Fe] and open
boxes indicate the average [(Si+Ca)/Fe]. For Si and Ca the trends
follow the solar neighborhood relation (solid line), whereas the
Mg and Ti abundances are enhanced by ~ 0.4 dex for most stars, similar
to the halo values.

Some overlap exists between the chemical properties of the
McWilliam & Rich
(1994)
bulge giant sample and the disk F dwarfs of
Edvardsson et al
(1993):
In general, the disk results
(Edvardsson et al 1993)
show that Mg and Ti are slightly enhanced relative to Si and Ca, which is
similar to, but less extreme than, the +0.4-dex enhancements of Mg and Ti
in the bulge.
Edvardsson et al (1993)
identified a subgroup of stars with 0.1-dex enhancements of Na, Mg, and Al;
these are conceivably related to the bulge giants, which have large Mg and
Al enhancements. The bulge [O/Fe] ratio is not well constrained: The extant
data are insufficient to determine whether oxygen behaves like Mg and Ti
or Si and Ca. However, any oxygen enhancement in the bulge must be less than
+0.5 dex (A McWilliam, A Tomaney & RM Rich, in preparation).

The unusual mixture of
-element abundances in
the bulge is evidence that
elements are made in
different proportions by different SN; i.e. there are different flavors
of SN with different
-element yields. This
conclusion is borne out by predicted
-element yields (e.g.
Woosley & Weaver
1995),
as shown in Figure 6.
Figure 6 illustrates that enhanced Mg could
occur with relatively more
35-M
SN progenitors than in the disk. The enhanced Ti is not explained by any
SN nucleosynthesis predictions.

Figure 6. Production factors from models of
SN II by
Woosley & Weaver
(1995).
Ejected element abundances for various progenitor masses are indicated
by connected symbols; O and Mg are produced in large
quantitiesat high mass (~ 35
M) but not in
the lower mass (15-25
M) SN,
which are responsible for most of the Si and Ca production. None of the
models give significant enhancements of Ti relative to Fe, contrary to
observations of stars in the Galactic bulge and halo. Note that
production factor is defined
as the ratio of the mass fraction of an isotope in the SN ejecta, divided
by its corresponding mass fraction in the Sun. The mass of the progenitor
making the indicated elements is given in the key in the upper right.

The Ti enhancements seen in bulge stars
present a nice qualitative explanation for the well-known phenomenon that
the spectral type of bulge M giants is later than disk M giants with the
same temperature.
Frogel & Whitford
(1987)
suggested that the later spectral types were due to overall
super-metallicity of the bulge stars;
McWilliam & Rich
(1994)
argued that the Ti enhancements are sufficient to create the stronger bulge
M giant TiO bands, without affecting overall metallicity. The enhanced Mg
abundances may also explain
Rich (1988)
high [Fe/H] results, which were based on measurements of the Mg b
lines and assumed that the bulge giants have the solar [Mg/Fe] ratio.

Unfortunately, the unusual mixture of
-element
abundances for the bulge makes it difficult to use these elements to
estimate the bulge formation time scale; the simple picture of SN Ia and
SN II implies a different time scale depending on which elements are
considered. However,
the observed Mg overabundances agree with the predictions of
(Matteucci &
Brocato 1990) and a rapid formation time scale for the bulge.

Multi-population synthesis analysis of low-resolution integrated light
spectra of the Galactic bulge by
Idiart et al (1996a)
indicated a mean bulge abundance ratio of [Mg/Fe] = +0.45 dex. Using the
same technique for elliptical galaxies and bulges of external spirals,
Idiart et al
(1996b) showed a general Mg enhancement of ~ +0.5 dex.
Worthey et al (1992),
using single-population models, analyzed spectra of giant elliptical
galaxies
and found Mg enhancements relative to Fe between +0.2 to +0.3 dex. These
results provide supporting evidence in favor of enhanced Mg in the bulge,
as claimed by
McWilliam & Rich
(1994).
An obvious question arising from the population synthesis results is whether
Ti is enhanced in external bulges and elliptical galaxies.

The abundance results for
elements in the bulge show that chemical abundance ratios are a function
of environmental parameters. In this regard, further study of the detailed
chemical composition of Galactic components will lead to an understanding
of how environment affects chemical evolution, which can be used to
interpret
low-resolution low-S/N spectra of distant galaxies. In particular, it is
necessary to check the
McWilliam & Rich
(1994)
results for O, Ca, and Si because results for these three elements are
less reliable than for Mg and Ti.